Laser emitters and photosensitive targets are widely used in industry for aligning machine components to one another. The prior art laser emitter projects a substantially straight beam toward the photosensitive target. The prior art target precisely identifies the location of the center of energy of the laser beam impinging thereon. Signals generated by the prior art photosensitive target can be used to accurately identify displacement errors and angular alignment errors between the prior art laser emitter and target.
The prior art combination of a laser emitter and a photosensitive target may be used, for example, to align a machine tool to a work piece. Displacement and angular alignment errors between the machine tool and the work piece can be determined by the prior art laser alignment equipment. Available laser alignment equipment also can mathematically convert the error readings into required adjustments on either the machine tool or the work piece. Correction of such errors ensures more accurately machined parts, longer tool life and less down-time for the machine tool. Very effective laser alignment systems for these purposes are disclosed in U.S. Pat. No. 4,566,202 which issued to the inventor herein on Jan. 28, 1986 for "LASER APPARATUS FOR EFFECTIVELY PROJECTING THE AXIS OF ROTATION OF A ROTATING TOOL HOLDER" and in copending patent application Ser. No. 427,759 which was filed by the inventor herein on Oct. 26, 1989 for "LASER ALIGNMENT CONTROL SYSTEM."
The prior art also has included laser emitters which are operative to sweep a substantially flat laser plane. A device of this type is shown and described in U.S. Pat. No. 4,468,119 which issued to the inventor herein on Aug. 28, 1984 and which is entitled "PENTA-PRISM MODULE HAVING LASER ALIGNMENT ERROR DETECTION AND CORRECTION CAPABILITY." The apparatus shown in U.S. Pat. No. 4,468,119 directs a laser beam to a penta-prism that is operative to reflect an input laser beam internally, and to produce an output beam aligned at precisely 90.degree. to the input beam. The penta-prism of the apparatus shown in U.S. Pat. No. 4,468,119 can be rotated about the axis of the input beam. Thus, the output laser beam from the rotating penta-prism effectively sweeps a plane that is perpendicular to the input beam. This plane can be used as a reference to which the alignment and/or position of other objects can be compared. For example, some machines are intended to have a plurality of coupled drive shafts disposed in end-to-end linear relationship defining, for example, the Z-axis. The apparatus shown in U.S. Pat. No. 4,468,119 can be used to sweep a plane parallel to the specified Z-axis of the coupled shafts to be aligned. Photocell targets may be fixtured simultaneously or sequentially at a plurality of locations along the coupled shafts to be aligned, and their respective Y-axis positions relative to the laser plane swept by the apparatus of U.S. Pat. No. 4,468,119 can be determined. Rotation of the penta-prism can be stopped to direct the diverted laser beam parallel to the specified Z-axis of the shafts. The X-axis offsets then can be measured. Selected shafts can be adjusted to achieve the required linear alignment.
Some prior art machines include components that should be aligned three dimensionally. For example, at least one coupling in the above described system of shafts may have a specified Z-axis location. The above described laser apparatus can be set up at location laterally offset from the specified Z-axis location. A beam can then be projected parallel to the X-axis, and the position of a target mounted on the coupling can be determined. Similar alignment problems occur in mills where a plurality of components are rotatably driven about parallel axes. Drive components for each of the rotatable members may be specified for disposition in a common Y-Z plane extending perpendicular to each of the respective rotational axes. Several of the rotatable members may be specified to lie in a common horizontal or X-Z plane, while others may be specified to lie in a vertical or X-Y plane. A complex machine of this type could include many alignment errors, any one of which could effect the quality of the finished product produced by the machine, the efficiency of the machine, the life of various components in the machine and the frequency of down-time for maintenance or repairs.
It can be difficult to perform all of the above described alignment checks with the prior art laser apparatus. In particular, some alignment checks must be performed sequentially with the prior art apparatus, and each sequential check may require a new setup of the laser alignment apparatus. It is desireable to minimize the number of setups and the time required for setups of the laser alignment machines.
Certain types of alignment checks will produce inaccurate results due to unavoidable errors in a target location relative to a component being aligned. For example FIG. 1 schematically shows a prior art target T mounted to a rod R and used with a prior art laser apparatus (not shown) to check the X-axis and Y-axis position of a shaft S. If the rod R is perfectly aligned along the Y-axis, positions of the shaft S can be determined. However, precise vertical alignment of the rod R generally cannot be assured, and an exaggerated non-vertical alignment is shown by the line R'. This inevitable offset of the rod R' will introduce errors into the X-axis and Y-axis readings of the target T'. The Y-axis error is indicated by dimension "a" in FIG. 1. This is referred to as a sine error, in that the magnitude of "a" is a function of the sine of the angle between R and R'. Sine errors generally are small enough to be tolerated. The X-axis error is indicated by dimension "b" and is a cosine error. Cosine errors can be very significant. The prior art laser apparatus used to check offsets relative to two axes typically would yield one reading subject to a cosine error.
In view of the above, it is an object of the subject invention to provide a versatile laser alignment apparatus that can be used to perform alignment in a broad range of both complex and simple industrial applications.
It is a further object of the subject invention to provide a laser alignment apparatus that minimizes setup time.
A further object of the subject invention is to provide a laser apparatus that avoids multiple setups for alignments.
Still an additional object of the subject invention is to provide laser alignment apparatus for comparing one or more objects to be aligned to a plurality of frames of reference simultaneously.
Yet a further object of the subject invention is to provide a laser apparatus that can avoid cosine errors.